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Explosive circuit breakers are standard in electric car safety systems (in case the regular one fails). I can't imagine anyone using them in normal operation th

by fsh 3y ago

Explosive circuit breakers are standard in electric car safety systems (in case the regular one fails). I can't imagine anyone using them in normal operation though. The space pen story is made up as well: https://www.snopes.com/fact-check/the-write-stuff/ https://www.snopes.com/fact-check/the-write-stuff/

trelane 3y ago
It's not quite wrong either. The truth is more complex. See https://www.scientificamerican.com/article/nasa-spent-millions-on-a-pen-able-t/ https://www.scientificamerican.com/article/nasa-spent-millio... and https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2MQ1RR https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2... I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). And the graphite conductivity problem is a non sequitur, given that the Russians used wax (or grease) pencils, not graphite. This is really the point of the anecdote: wasteful government spending. Though apparently the Russians also find the pens useful and bought some as well.
- kube-system 3y ago
  > I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). Only people who don't understand how engineering and manufacturing projects work. $1300 is completely reasonable for a very low volume manufactured product, which was specified to meet specific criteria. The reason it sounds unreasonable is because it is being called a "pencil/pen", instead of what it actually was, which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. At face value in meme format, the implied "free" solution would be buying a pen or pencil off the shelf, when in reality, that alone wouldn't have solved the problem. It is possible that someone could have evaluated off-the-shelf options to see if one would have met the criteria, but that would still have significant labor cost.
  - trelane 3y ago
    > which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. Right, that's the point. It's also how you get the other very expensive things that the Pentagon gets dinged for.
- Retric 3y ago
  What everyone forgets is how valuable each second of astronaut time actually is. 1300$ for a slightly better pen is probably a great deal for the agency. The shuttle program (excluding ISS) worked out to roughly 1 million dollars each hour an astronaut spent in space including when they were sleeping. Space stations are significantly better but anything that marginally improves astronaut effectiveness is worth quite a bit.
- eternityforest 3y ago
  But those space pens are available to civilians now. In plastic disposable versions for a few bucks(uniball power tank). They are the only pens I know that stand up to modern use where you might only touch them once a week or less. Now they exist, and probably will be available indefinitely, and cheaply, and the problem of pens that just work anywhere is basically solved. Isn't part of the point of NASA to develop tech that benefits everyone? Granted it's not a major life changing thing, but it's not just tossing money in the toilet either.
amluto 3y ago
As I understand it, the point of the explosive is to have finer control over when the fuse blows. An ordinary fuse is more or less a resistor, and it blows when part of it gets hot enough. There is a fair amount of error, and this means they work best when there is a considerable margin between the current they must carry without blowing and the conditions under which they must blow. Conventional thermal-magnetic or hydraulic-magnetic circuit breakers are similar. AIUI some high performance cars may draw so much current under maximum acceleration that the fuse needs to be dangerously large to avoid blowing when flooring it. The solution is an electronically triggered fuse. A reliable and precise electronic circuit detects excessive current and blows a small pyrotechnic charge that opens the fuse. The analogous technology for circuit breakers is fairly mature in the commercial/industrial world — you can buy an electronically tripped circuit breaker, and there is likely one in an office building near you. (Electronic trip devices for circuit breakers have ludicrous list prices, and there is no way a car company would pay anything resembling those prices for a car component that lets them eke out a bit more performance. I bet Tesla’s cost for its pyro fuses is quite low.)
- quickthrowman 3y ago
  > Electronic trip devices for circuit breakers have ludicrous list prices The last one I bought was a GFCI trip unit for a 1000A 480v Siemens breaker and it was around $6000, and that doesn’t include the cost of the circuit breaker.
  - amluto 3y ago
    That's pretty impressively expensive, especially given that the innards should not have any particular dependence on the rated current. (I suppose the GFCI sensing circuit needs to tolerate an increased amount of induced current as the available fault current goes up.)

by fsh 3y ago

trelane 3y ago

It's not quite wrong either. The truth is more complex. See https://www.scientificamerican.com/article/nasa-spent-millions-on-a-pen-able-t/ https://www.scientificamerican.com/article/nasa-spent-millio... and https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2MQ1RR https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2... I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). And the graphite conductivity problem is a non sequitur, given that the Russians used wax (or grease) pencils, not graphite. This is really the point of the anecdote: wasteful government spending. Though apparently the Russians also find the pens useful and bought some as well.

kube-system 3y ago
> I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). Only people who don't understand how engineering and manufacturing projects work. $1300 is completely reasonable for a very low volume manufactured product, which was specified to meet specific criteria. The reason it sounds unreasonable is because it is being called a "pencil/pen", instead of what it actually was, which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. At face value in meme format, the implied "free" solution would be buying a pen or pencil off the shelf, when in reality, that alone wouldn't have solved the problem. It is possible that someone could have evaluated off-the-shelf options to see if one would have met the criteria, but that would still have significant labor cost.
- trelane 3y ago
  > which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. Right, that's the point. It's also how you get the other very expensive things that the Pentagon gets dinged for.
Retric 3y ago
What everyone forgets is how valuable each second of astronaut time actually is. 1300$ for a slightly better pen is probably a great deal for the agency. The shuttle program (excluding ISS) worked out to roughly 1 million dollars each hour an astronaut spent in space including when they were sleeping. Space stations are significantly better but anything that marginally improves astronaut effectiveness is worth quite a bit.
eternityforest 3y ago
But those space pens are available to civilians now. In plastic disposable versions for a few bucks(uniball power tank). They are the only pens I know that stand up to modern use where you might only touch them once a week or less. Now they exist, and probably will be available indefinitely, and cheaply, and the problem of pens that just work anywhere is basically solved. Isn't part of the point of NASA to develop tech that benefits everyone? Granted it's not a major life changing thing, but it's not just tossing money in the toilet either.

amluto 3y ago

As I understand it, the point of the explosive is to have finer control over when the fuse blows. An ordinary fuse is more or less a resistor, and it blows when part of it gets hot enough. There is a fair amount of error, and this means they work best when there is a considerable margin between the current they must carry without blowing and the conditions under which they must blow. Conventional thermal-magnetic or hydraulic-magnetic circuit breakers are similar. AIUI some high performance cars may draw so much current under maximum acceleration that the fuse needs to be dangerously large to avoid blowing when flooring it. The solution is an electronically triggered fuse. A reliable and precise electronic circuit detects excessive current and blows a small pyrotechnic charge that opens the fuse. The analogous technology for circuit breakers is fairly mature in the commercial/industrial world — you can buy an electronically tripped circuit breaker, and there is likely one in an office building near you. (Electronic trip devices for circuit breakers have ludicrous list prices, and there is no way a car company would pay anything resembling those prices for a car component that lets them eke out a bit more performance. I bet Tesla’s cost for its pyro fuses is quite low.)

quickthrowman 3y ago
> Electronic trip devices for circuit breakers have ludicrous list prices The last one I bought was a GFCI trip unit for a 1000A 480v Siemens breaker and it was around $6000, and that doesn’t include the cost of the circuit breaker.
- amluto 3y ago
  That's pretty impressively expensive, especially given that the innards should not have any particular dependence on the rated current. (I suppose the GFCI sensing circuit needs to tolerate an increased amount of induced current as the available fault current goes up.)